This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. During exercise the sympathetic system adjusts blood pressure, heart rate, ventilation and peripheral vasoconstriction. Circulatory adjustments are required to maintain proper profusion to vital organs during increased demands of muscles. Due to technical limitations sympathetic control over coronal hemodynamic responses in humans has not been possible. The noninvasive Doppler ultrasound technique has recently made this assessment possible. Thus, the aim of this study is to assess coronary blood flow during exercise. Modifying effects of age, gender (menstrual cycle) and heart failure will also be assessed. Finally, assessment will also be completed in heart and kidney transplant patients to discriminate between coronary vasoconstriction and myogenic autoregulation response.